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An RF coil system for magnetic resonance applications includes a
multi-channel RF coil transceiver and a multi-channel RF coil. The RF
coil system is structured for reconfiguration between a plurality of
operational modes.

GOVERNMENT RIGHTS The present subject matter was partially supported
under NIH contract numbers EB000895-04 and EB006835. The United States
government may have certain rights in the invention.

Claims

1. An RF coil system for magnetic resonance applications, comprising a
multi-channel RF coil transceiver and a multi-channel RF coil, the RF
coil system being structured for reconfiguration between a plurality of
operational modes.

2. The RF coil system of claim 1, wherein the at least one of the
plurality of operational modes is a quadrature mode.

3. The RF coil system of claim 1, wherein the at least one of the
plurality of operational modes is an adjustable multi-channel mode.

4. The RF coil system of claim 1, wherein the at least one of the
plurality of operational modes is a single tuned mode.

5. The RF coil system of claim 1, wherein the at least one of the
plurality of operational modes is a double tuned mode.

6. The RF coil system of claim 5, wherein the double tuned mode includes a
first frequency in a fixed mode and an operational frequency in a
multi-channel mode.

7. The RF coil system of claim 1, wherein the at least one of the
plurality of operational modes is a multi-nuclear, multi-channel mode
with at least one operational frequency driven in a multi-channel mode.

8. The RF coil system of claim 1, wherein the at least one of the
plurality of operational modes is a transmit mode.

9. The RF coil system of claim 1, wherein the at least one of the
plurality of operational modes is a receive mode.

15. The RF coil system of claim 1, wherein the RF coil is a body coil.

16. The RF coil system of claim 1, wherein the RF coil is a head coil.

17. The RF coil system of claim 1, wherein the RF coil is a TEM coil that
includes one or more independent transmission line elements.

18. The RF coil system of claim 1, further comprising an additional RF
coil.

19. The RF coil system of claim 18, further comprising a third coil,
wherein the RF coil, the additional RF coil, and the third coil are
electrically and mechanically integrated.

20. The RF coil system of claim 1, wherein the at least one of the
plurality of operational modes is a fixed mode.

21. The RF coil system of claim 1, wherein at least two of the plurality
of operational modes differ from each other in at least one of the
parameters selected from the group consisting of magnitude, frequency,
phase, time, and space.

22. A magnetic resonance imaging system, comprisinga superconducting
magnet;a gradient coil system; andan RF coil system comprising a
multi-channel RF transceiver and a multi-channel RF coil, the RF coil
system being structured for reconfiguration between a plurality of
operational modes.

23. A method for magnetic resonance imaging, comprising:providing a
magnetic resonance imaging apparatus including an RF coil
system;positioning a patient in the magnetic resonance imaging
apparatus;imaging the patient with the RF coil system in a first
operational mode; andimaging the patient with the RF coil system in a
second operational mode;wherein the patient remains positioned in the
magnetic resonance imaging apparatus during and between imagings in the
first and second operational modes.

[0002]The present disclosure relates generally to radio frequency (RF)
coils for RF field generation and detection, and more particularly, to RF
coils used for magnetic resonance imaging.

BACKGROUND

[0003]Nuclear magnetic resonance (NMR) or magnetic resonance imaging
(MRI), functional MRI (fMRI), electron spin resonance (ESR) or electron
paramagnetic resonance (EPR) and other imaging techniques using RF field
generating coils are finding increasing utility in applications involving
imaging of various parts of the human body, of other organisms, whether
living or dead, and of other materials or objects requiring imaging or
spectroscopy. There is an ongoing need for new and improved RF coils
and/or methods of operating RF coils.

SUMMARY

[0004]The present disclosure relates generally to radio frequency (RF)
coils for RF field generation and detection, and more particularly, to RF
coils used for magnetic resonance imaging.

[0005]In one aspect, the present disclosure provides an RF coil system for
magnetic resonance applications. The RF coil system includes a
multi-channel RF coil transceiver and a multi-channel RF coil. The RF
coil system is structured for reconfiguration between a plurality of
operational modes.

[0006]In another aspect, the present disclosure provides a magnetic
resonance imaging system that includes a superconducting magnet, a
gradient coil system, and an RF coil system. The RF coil system includes
a multi-channel RF transceiver and a multi-channel RF coil. The RF coil
system is structured for reconfiguration between a plurality of
operational modes.

[0007]In yet another aspect, the present disclosure provides a method for
magnetic resonance imaging. The method includes providing a magnetic
resonance imaging apparatus including an RF coil system, positioning a
patient in the magnetic resonance imaging apparatus, imaging the patient
with the RF coil system in a first operational mode, and imaging the
patient with the RF coil system in a second operational mode. In this
method, the patient remains positioned in the magnetic resonance imaging
apparatus during and between imagings in the first and second operational
modes.

[0008]The above summary is not intended to describe each and every
disclosed embodiment or every implementation of the disclosure. The
Description that follows more particularly exemplifies the various
illustrative embodiments.

BRIEF DESCRIPTION OF THE FIGURES

[0009]The following description should be read with reference to the
drawings. The drawings, which are not necessarily to scale, depict
selected embodiments and are not intended to limit the scope of the
disclosure. The disclosure may be more completely understood in
consideration of the following detailed description of various
embodiments in connection with the accompanying drawings, in which:

[0010]FIG. 1 is a schematic diagram of an illustrative magnetic resonance
imaging system;

[0011]FIG. 2 is a flowchart showing an illustrative method for magnetic
resonance imaging; and

[0012]FIG. 3 is a schematic diagram of an illustrative RF coil system.

DESCRIPTION

[0013]The following description should be read with reference to the
drawings. The drawings, which are not necessarily to scale, depict
selected embodiments and are not intended to limit the scope of the
invention. Although examples of construction, dimensions, and materials
are illustrated for the various elements, those skilled in the art will
recognize that many of the examples provided have suitable alternatives
that may be utilized.

[0014]Magnetic resonance imaging and a variety of other imaging techniques
employ RF coils. The mechanical and electrical configuration, or mode, of
an RF coil, along with the manner in which it is used, may generally
affect the imaging capabilities of the imaging system of which the coil
is a component. One RF coil mode may be suited for a whole body survey,
for example, while another RF coil mode may allow higher quality imaging
of a targeted body organ, which may have been identified as a target of
interest in a prior survey. Yet another RF coil mode may be suited for
spectroscopy of a portion of a targeted body organ, to detect, for
example, metabolic products or signatures. In general, for a given
imaging task, there may be an RF coil mode that is more suited for the
imaging task than alternative RF coil modes. Furthermore, for treatment,
diagnosis, or investigation of a subject, such as a medical patient, it
may be desirable to image the subject with a number of different coil
modes during a single session. Previously, switching RF coils has often
been a time-consuming and laborious process, which has generally
prevented single-session imaging with multiple coil modes. The present
disclosure provides improvements to the ease and speed with which RF coil
modes can be switched.

[0015]FIG. 1 is a schematic diagram of an illustrative magnetic resonance
imaging system 100 in accordance with the present disclosure. MRI system
100 may be used to image a subject or patient 102. MRI system 100
includes a superconducting magnet 104 and gradient coils 106 that are
coupled to gradient coil control components 108. The system 100 also
includes an RF coil system that includes a multi-channel RF coil 110
connected to a multi-channel RF transceiver 120. The RF coil system may
be switched between operational modes as described further herein.
Gradient control components 108 and multi-channel RF transceiver 120 are
connected to MRI system controller 130. MRI system 100 may include other
components, such as an additional RF coil 140, which may be any suitable
RF coil, including a multi-channel RF coil. Additional RF coil 140 may be
considered a part of the RF coil system that includes multi-channel RF
coil 110 and multi-channel RF coil 120. Additional RF coil 140 may be
connected to an RF coil transceiver 150, or it may be connected to
multi-channel RF coil transceiver 120, or it may be connected to any
other suitable driving and/or receiving component. The additional RF coil
140 may be a transmit and/or receive coil. Additional RF coils may be
useful for particular anatomical imaging tasks, and may be spatially
located proximate to targeted anatomical regions, such as a head, foot,
pelvis, etc., of a patient. In some embodiments, any or all of gradient
coils, RF coils, additional RF coils, shim coils, and any other suitable
coils may be electrically and/or mechanically integrated.

[0016]FIG. 2 is a flowchart showing an illustrative method 200 for
magnetic resonance imaging in accordance with the present disclosure. An
MRI apparatus, including an RF coil system, is provided as shown at block
210. A patient is positioned in the MRI apparatus at block 220. At block
230, the patient is imaged, with the RF coil system in a first
operational mode. At block 240, the patient is imaged, with the RF coil
system in a second operational mode. Further imagings in further
operational modes may be performed, up to an imaging in an Nth
operational mode as indicated at block 250. All imagings 230, 240, and
250 are performed during the same MRI session, with the patient remaining
positioned in the MRI apparatus during and between the imagings.

[0017]FIG. 3 is a schematic diagram of an illustrative RF coil system 300
that may be switched between operating or operational modes in accordance
with the present disclosure. RF coil system 300 may be employed in an MRI
system such as system 100 of FIG. 1, in which case it is employed as the
coil 110 and transceiver 120 of that system. The RF coil system 300
includes a multi-channel RF coil 310 and a multi-channel RF coil
transceiver 320. The multi-channel RF coil transceiver 320 may be
connected to an MRI system controller 330. MRI system controller 330 may
be coupled to multi-channel RF coil 310 through other mean as well.
Either or both of transceiver 320 and coil 310 may have 1, 2, 4, 8, 16,
32, 64, or any other suitable number N of channels. The numbers of
channels for the transceiver 320 and coil 310 may be the same, or it may
be different. In some RF coil systems, there is a one-to-one
correspondence between transceiver channels and coil channels, which may
also be referred-to as coil elements. In some RF coil systems, the number
of transceiver channels is less than the number of coil channels or
elements.

[0018]RF coil transceiver 320 may be a transceiver as described in U.S.
Pat. No. 6,969,992 ("PARALLEL TRANSCEIVER FOR NUCLEAR MAGNETIC RESONANCE
SYSTEM," Vaughan et al.), which is hereby incorporated by reference, or
it may be any other suitable RF transceiver. In some RF coil systems,
more than one RF coil transceiver may be associated or connected with an
RF coil. In some RF coil systems, an RF coil transceiver may be
associated with more than one RF coil. RF coil transceivers may allow
control of RF amplitude, frequency, phase, and timing for individual or
multiple coil channels or elements. RF coil transceivers may be
configured both for excitation of RF fields in RF coils, as well as
reception of RF signals from RF coils. Selection between excitation
(transmission) and reception modes may be made for individual channels,
or collectively for sets of channels or for all channels.

[0019]RF coil 310 may be an RF coil as described in U.S. Pat. No.
6,633,161 ("RF COIL FOR IMAGING SYSTEM," Vaughan), which is hereby
incorporated by reference, or it may be any other suitable RF coil.
Suitable coils include, but are not limited to, coils having
multi-channel arrays, including TEM coils including one or more
independent transmission line elements, stripline arrays, microstrip
arrays, transmission line arrays, and the like. In some cases, the coils
may have independent phase and magnitude control. RF coil 310 may be a
volume coil, generally defined as a coil with a plurality of current
elements surrounding a volume containing an NMR active sample, or a
surface coil, generally defined as a coil with one or more elements
adjacent to an NMR active sample. RF coil 310 may be a coil structured
appropriately for imaging of a particular external or internal anatomical
region, such as the head, knee, elbow, breast, heart, etc., or it may be
a body coil for imaging substantially an entire body or major subportion
of a body. RF coil 310 may include one or more independent current
elements, on which field generating currents may be controlled in
magnitude, phase, frequency, space, and time.

[0020]RF coils systems as described herein may be useful for human head
and body imaging at high magnetic field strengths, but are not
necessarily limited to such high magnetic field strengths. RF coil
systems of the present disclosure may be used in imaging systems
employing magnetic field strengths of 1.5 T, 4 T, 4.1 T, 7 T, 8 T, 9.4 T,
and any other suitable field strengths.

[0021]RF coil systems of the present disclosure may be operated in
multiple operational modes and may be conveniently switched between the
modes. A number of operational modes are described herein, however, it is
contemplated that any other suitable operational modes may be used with
RF coil system of the present disclosure. In general, operational modes
may be transmit modes or receive modes. In the present disclosure,
switching or reconfiguring modes does not include simply switching from a
transmit mode to a receive mode, or vice versa, without any other change
in mode configuration.

[0022]An RF coil system of the present disclosure may be operated in a
single tuned, reactively coupled (driven) operational mode. A field
generating and/or receiving current element of an RF coil is reactively
coupled for RF signal transmit or receive operation when a current is
inductively or capacitively excited in said element. A typical example of
a reactively coupled RF coil will include a plurality of current elements
containing one are more directly coupled elements which reactively excite
(transmit to) or receive signal from one or more reactively coupled
elements surrounding (volume) or adjacent to (surface) an NMR active
sample. This mode may be a fixed quadrature mode, or it may be any other
suitable mode.

[0023]An RF coil system of the present disclosure may be operated in a
single tuned, directly coupled operational mode. A field generating
and/or receiving current element of an RF coil is directly coupled for RF
signal transmit or receive operation when a current is directly
transmitted to or received from said element by means of a signal
carrying conductor attached to said element. A typical example of a
directly coupled RF surface coil or volume coil will include one or more
directly coupled elements which excite (transmit to) or receive signal
from an NMR active sample. This mode may be a fixed quadrature mode, or
it may be any other suitable mode.

[0024]An RF coil system of the present disclosure may be operated in a
dual tuned, reactively coupled operational mode. A typical example of
this operational mode includes a surface or volume coil with one subset
of one or more current elements tuned to one frequency, and another
subset of one or more elements tuned to another frequency. At least some
of the elements tuned to each frequency are reactively coupled to one or
more directly coupled elements for each frequency.

[0025]An RF coil system of the present disclosure may be operated in a
dual tuned, or double-tuned, directly coupled operational mode. A typical
example of this operational mode includes a surface or volume coil with
one subset of one or more current elements tuned to one frequency, and
another subset of one or more elements tuned to another frequency.

[0026]In general, directly coupled operational modes may also be referred
to as adjustable multi-channel modes, where a multi-channel RF
transceiver allows adjustment to RF signals in multiple channels
simultaneously in multiple degrees of freedom, including magnitude,
frequency, phase, and timing of RF signal. Adjustable multi-channel modes
may be single tuned, double tuned, or may involve greater than two RF
frequencies.

[0027]An RF coil system of the present disclosure may be operated in a
hybrid operational mode. A typical example of this operational mode
includes a surface or volume coil with one subset of one or more elements
reactively coupled, and another subset of one or more elements directly
coupled. In this hybrid operational mode, one subset of reactively
coupled elements may be tuned to one frequency, and another subset of
directly coupled elements may be tuned to another frequency.

[0028]In an illustrative embodiment, a body coil may be built on a single
form, with the ability to switch the mode of operation of the coil
between a single tuned, reactively coupled operational mode, a single
tuned, directly coupled operational mode, and a hybrid operational mode.
In the single tuned, reactively coupled operational mode, the body coil
has four symmetrically spaced, directly coupled elements which in turn
are reactively coupled to the remaining elements of the coil. In this
mode, the elements may be driven at one Larmor (proton) frequency, with
equal magnitude, and with circularly polarized phasing. This circularly
polarized, quadrature phased, body coil mode may replace, for example,
conventional birdcage design body coils. This mode may be considered a
fixed quadrature mode. In switching to the single tuned, directly coupled
operational mode, all or a fraction of these elements could be switched
to a direct drive configuration. Direct control over the currents in the
independent coil elements, as made possible by a multi-channel RF coil
transceiver (as described in, for example, U.S. Pat. No. 6,969,992),
facilitates B1 field shimming, localization, scanning, transmit SENSE,
frequency hopping, and other applications benefits. From this operational
mode, a fraction of the coil current elements could be switched to a
second frequency. In the hybrid operational mode, the coil configuration
may use a first set of directly coupled (driven) current elements for MRI
at the higher proton Larmor frequency where more B1 field control is
required for optimal imaging, and a second set of reactively coupled
current elements at a lower "X nuclei" Larmor frequency where a
circularly polarized field would achieve good magnetic resonance
spectroscopy (MRS) results.

[0029]RF coil systems of the present disclosure may be operated in any
suitable operational modes. One operational mode is a double tuned mode
including a first frequency in a fixed mode and an operational frequency
in a multi-channel mode. Another operational mode is a multi-nuclear,
multi-channel mode with at least one operational frequency driven in a
multi-channel mode.

[0030]In an illustrative embodiment of the present disclosure, an RF coil
system is switched between operational modes. The operational modes are
distinguished from each other by differences in one or more of the
following RF parameters: magnitude, frequency, phase, time, and space
(i.e., location of coil elements, coils, or subcoils). Any permutation or
combination of differences in these parameters may be included.

[0031]In exemplary embodiments of the present disclosure, multi-channel RF
coil systems may be switched between any suitable combinations of
operational modes. In one example, a multi-channel RF coil system may be
switched from a fixed quadrature excitation mode, to an adjustable
multi-channel excitation mode. In one example, a multi-channel RF coil
system can be switched from a fixed quadrature excitation mode, to an
adjustable multi-channel excitation mode. In one example, a multi-channel
RF coil system can be switched from a fixed, single tuned quadrature mode
to a fixed, double tuned quadrature mode of operation. In one example, a
multi-channel RF coil system can be switched from a fixed, single tuned
quadrature mode to a fixed, double tuned quadrature mode of operation. In
one example, a multi-channel RF coil system can be switched from a fixed
quadrature mode, to an adjustable multi-channel mode, to a double tuned
mode with one frequency in fixed mode and one operational frequency
driven in multi-channel mode for the coil. In one example, a
multi-channel RF coil system can be switched from a fixed quadrature
mode, to an adjustable multi-channel mode, to a double tuned mode with
one frequency in fixed mode and one operational frequency driven in
multi-channel mode for the coil. In one example, a multi-channel RF coil
system can be switched from a fixed quadrature mode, to an adjustable
multi-channel mode, to a multi-nuclear, multi-channel mode with
operational frequency(s) driven in multi-channel mode for the coil. In
one example, a multi-channel RF coil system can be switched from a fixed
quadrature mode, to an adjustable multi-channel mode, to a multi-nuclear,
multi-channel mode with operational frequency(s) driven in multi-channel
mode for the coil.

[0032]In one example, the multi-channel RF coil system includes a body
coil that can be switched from "conventional" drive quadrature mode, to
multi-channel mode, to "hybrid" multi-nuclear mode. In one example, the
multi-channel RF coil system includes a TEM body coil that can be
switched from "conventional" drive quadrature mode, to multi-channel
mode, to "hybrid" multi-nuclear mode. In one example, the multi-channel
RF coil system includes a body coil that can be switched from
"conventional" drive quadrature mode, to multi-channel mode, to
multi-channel, multi-nuclear mode. In one example, the multi-channel RF
coil system includes a TEM body coil that can be switched from
"conventional" four port drive quadrature mode, to multi-channel mode, to
multi-channel, multi-nuclear mode. In one example, the multi-channel RF
coil system includes a body coil that can be switched from "conventional"
drive quadrature mode, to multi-channel mode. In one example, the
multi-channel RF coil system includes a TEM coil that can be switched
from "conventional" drive quadrature mode, to multi-channel mode. Any
other suitable combination of operational modes described herein may be
employed in RF coil systems of the present disclosure.

[0033]In exemplary embodiments of the present disclosure, any suitable
combinations of operational modes may be achieved in single form factor
RE coils. Such RF coils may be volume or surface coils, and they may be
body coils or coils intended for imaging body parts such as the head.

[0034]RF coil current elements are described in this disclosure as being
"reactively coupled" or "directly coupled." The coupling of a "directly
coupled" current element may include reactive components between the
current element and the RE transceiver, generally for the purpose of
impedance matching, and thus the "directly coupled" current element may
be, strictly speaking, reactively coupled to the RF transceiver and it
may be driven reactively. For the purposes of this disclosure, however,
one of skill in the art will recognize that a "reactively coupled"
current element of an RF coil is a current element that is coupled to an
other current element of the RF coil through inductance and capacitance,
where the other current element of the RF coil is a current element
capable of transmitting and/or receiving significant RF radiation to or
from an NMR active sample, and which is designed to effect such
transmission and/or reception. A "reactively coupled" current element
communicates electrically with an RF transceiver through such an other
current element and does not significantly communicate electrically with
an RF transceiver without the intervening other current element.

[0035]Some exemplary RF coils of the present disclosure include reactively
decoupled coil elements. Some exemplary RF coils of the present
disclosure include reactively coupled coil elements. In such coils with
reactively coupled coil elements, reactive coupling between some or all
coil elements may be suppressed. Suppression of reactive coupling may be
achieved by any suitable method, including those described in U.S. Pat.
No. 6,633,161. Some exemplary coils may achieve suppression of reactive
coupling with lumped element bridging or without lumped element bridging.
Suppression of reactive coupling may also be achieved with distributed
reactance cancellation, as described in, for example, U.S. Pat. No.
6,633,161.

[0036]Switching or reconfiguring between operational modes of a
multi-channel RF coil system may be achieved through any suitable method
and with any suitable means. In some cases, switching modes may be
achieved substantially or entirely by configuration of the multi-channel
RF transceiver associated with the multi-channel RF coil of a
multi-channel RF coil system. In some cases, such configuration may be
commanded or coordinated by or from an MRI system controller. In some
cases, switching modes may include directly and/or reactively coupling or
decoupling coil elements of a multi-channel RF coil. Coupling and
decoupling may be accomplished by orienting the spatial position of coil
elements relative to each other, by manipulating the electrical phase
relations of coil elements relative to each other, by changing the field
amplitude of coil elements relative to each other, by changing the
resonant frequency of coil elements relative to each other and/or by
temporal separation of the field of coil elements relative to each other
by any combination of the above techniques. Discrete, lumped, or
distributed capacitance and/or inductance may be added, removed, coupled,
or decoupled to any or all coil elements. Furthermore, mechanical means,
including relative spatial manipulations of the coil elements or
mechanical switching or reorienting of the phase, amplitude and/or
frequency of coil elements, current, voltage and RF fields might be
utilized to effect coupling and/or decoupling of coil elements.
Electrical or electronic control of coupling or decoupling may be by PIN
diodes, solid state switches such as transistors, and semiconductor
relays, tube switches, electromechanical relays, varistors, and the like.
In addition to the "active" electronic components indicated above,
"passive" components may also be used, including small signal diodes,
limiter diodes, rectifier diodes, etc., these components often being used
together with quarter-wave circuits. Switching operational modes of an RF
coil system may involve any appropriate combination of configuration of
the multi-channel RF transceiver and electrical, electronic,
electromechanical, mechanical, or any other modification to the
configuration of the multi-channel RF coils. In some embodiments, all
steps in switching operational modes of an RF coil system may be
commanded and/or controlled by the MRI system controller of the MRI
system.

[0037]Hardware configurations that may be used in the practice of the
present disclosure are described herein.

[0038]Hardware has been developed for 7T equipment. The MRI system may be
a Magnex 7T, 90 cm bore magnet with Siemens whole body gradients and
shims (i.d.=63 cm). A Siemens 7T console may be used, together with a
custom 16 kW, 16 channel, solid state transmitter from Communications
Power Corporation (CPC). An actively detuned, 300 MHz. RF body coil was
built together with its PIN detuning circuits and system control
interface. Specialty 300 MHz receive circuits, such as a 6-element
stripline dual breast array, were developed together with the necessary
PIN decoupling circuits and multi-channel, digital receivers.

[0039]A custom 16 kW, 16 channel, solid state transmitter from
Communications Power Corporation (CPC) may be employed in multiple
configurations. In one mode, 16 channels may be used over a frequency
range from 30-405 MHz with 1 kW available per channel. This mode may be
employed, for example, for proton frequency imaging of targeted organs.
In another mode, two channels may be used over a frequency range from
30-405 MHz with 6 or 7 kW available per channel, depending on gain
linearity requirements. This mode may be employed, for example, for two
nucleus imaging. In yet another mode, one channel may be used over a
frequency range from 30-405 MHz with 10.5 or 11.5 kW available per
channel, depending on gain linearity requirements. This mode may be
employed, for example, for circularly-polarized global scouting imaging.

[0040]In some cases, an illustrative RF coil included an eight-channel,
flexible, transceiver array built according to stripline transmission
line (TEM) principles. This eight-channel coil included of a pair of
four-element TEM arrays, one to be located anterior and the other
posterior to the pericardium. Four coil elements each were attached in
parallel configuration to a flexible PTFE plate measuring 22.7
cm.times.35.6 cm.times.0.3 cm thick. The individual coil elements were
15.3 cm long with a 1.27 cm wide inner conductor and a 5.0 cm wide outer
conductor, separated by a 1.9 cm thick PTFE dielectric bar stock with a
low loss tangent and a permittivity of 2.08. A 4.3 cm air gap separated
each coil element.

[0041]In some cases, each element were individually tuned to 297 MHz (7T),
and matched to a 50 ohm, coaxial TR signal line. Capacitive decoupling
facilitated greater than 18 dB isolation between elements for the
unloaded coil.

[0042]Imaging experiments were performed on a 7T (.omega..sub.o=297.14
MHz) magnet (Magnex Scientific, UK) interfaced to a Siemens console and
whole body gradients. The output of an 8 kW RF power amplifier (CPC,
Brentwood, N.Y.) was divided into the eight channels of equal magnitude
and phase to feed an eight element coil (Werlatone, Brewster, N.Y.).
Eight high-power phase shifters, (ATM, Patchogue, N.Y.) and incremental
cable lengths were used to adjust the transmit phase as required to
accomplish B.sub.1 shimming for optimal image homogeneity over the heart
region. Power divider specifications included -0.4 dB insertion loss and
1.degree. phase resolution, while the phase shifters measured -0.5 dB
insertion loss over a phase range of 120.degree..

[0043]In some methods, local B.sub.1 shimming was used. To optimize the RF
field uniformity and RF transmit and receive efficiency for the heart,
the transmitted "B.sub.1.sup.+" field components of the independent coil
elements were adjusted or "shimmed" to effect an approximate phase
coherence or "constructive interference" of the short RF wavelengths (12
cm) over the region of interest. To adjust the phase angle of the RF
current and resultant B.sub.1 field generated by each element, an
excitation pulse was transmitted through one channel at a time while the
other transmit channels were terminated with 50.OMEGA. loads. The
feedback signal was received from all eight channels during this stepwise
transmit field shimming process. The relative transmit B.sub.1.sup.+
phases were then calculated using a low resolution, low flip angle
gradient echo (GRE) images

[0044]In one example, the MRI system used for a study was built around a
Magnex 7 T, 90 cm bore magnet (Magnex Scientific, Oxfordshire, UK)
equipped with a Sonata gradient system (Siemens, Erlangen, Germany).
Interfaced to this magnet was a Unity Inova spectrometer (Varian, Palo
Alto, Calif.), together with a custom, 8 kW solid-state RF power
amplifier (Communications Power Corporation (CPC), Hauppauge, N.Y.). The
whole body images in this report were acquired with an actively
detuneable 300 MHz transverse electromagnetic (TEM) body coil. Also
developed was an eight channel TEM surface coil. For imaging the human
trunk, these surface coils were used in pairs anterior and posterior to
the body region of interest. The elements of these multi-channel,
transmit and receive coils were driven independently from a new 16
channel, parallel transceiver designed in-house and built by CPC. This
system enabled B.sub.1 phase and magnitude control of each of the coil's
16 independent elements to facilitate B.sub.1 shimming and parallel
imaging methods. A circularly-polarized, unilateral RF breast coil
consisting of two shielded crossed loops was also built and tested.

[0045]In another example, body imaging with Multi-channel TEM Surface Coil
was performed. Employing multi-channel transceiver coils closely fitted
to the body offered an alternative to whole body coils for imaging
localized regions of interest. With this coil, a phase and gain
controlled transmit signal was delivered to each independent element. In
turn, signal was received from each element through a TR switch, and
combined by sum-of squares or other image reconstruction algorithm. RF
power was monitored for each channel.

[0046]In another example, breast imaging and spectroscopy with Quadrature
Surface Coil was performed. MRI and MRS data were acquired from a healthy
normal female volunteer using a transceiver surface coil. To distinguish
fibro-glandular from adipose tissue, T.sub.1-weighted images were
acquired using fat-suppressed 3D FLASH. Acquisition parameters were:
TR/TE=15/5 ms, FOV=14 cm, and matrix=256.times.256.times.64. Single-voxel
spectra were collected using the LASER pulse sequence (20) and TE
averaging. To quantify fibro-glandular choline containing compounds, the
unsuppressed water signal in the voxel was used as an internal reference.
LASER localization was used to achieve VOI=1.6 mL, TR=3 s, TE=43-195 ms
in 128 increments, and 8 Hz line broadening.

[0047]Not all "body" imaging is best served with a body coil. Cardiac
imaging and spectroscopy can gain greatly from the temporal, spatial, and
spectral resolution inherent to 7T. Significant improvements in heart
image SNR and B.sub.1 uniformity were achieved by using a multi-channel
transceiver, together with B.sub.1 shimming. The local SAR required for
these improved surface coil images was approximately the same 1 W/kg used
to acquire the body images. Use of local, multi-channel, transceiver
coils with B.sub.1 shimming has proven successful in 7T prostate imaging
as well.

[0048]For local imaging and spectroscopy of more superficial anatomy such
as the breasts, more conventional transceiver surface coils can be used
effectively. Early results from a 7 T breast cancer study gives example
for the promise of 7 T diagnostics. Measurement of total
choline-containing compounds (tCho) by localized .sup.1H MRS offers a
means to distinguish malignant from benign lesions and to predict
response to neoadjuvant chemotherapy. The detection of tCho in small
lesions having low cellularity is usually limited by insufficient SNR at
clinical field strengths. Previous breast MRS studies at 4 T have
reported higher SNR, enabling the detection of tCho in smaller lesions as
well as the occasional detection of other metabolites such as taurine,
creatine, and glycine. The ability to detect relatively narrow tCho and
Taurine resonances in normal breasts provides motivation to pursue future
7 T studies of breast cancer.

[0049]First examples of theoretical models, technology and methods for
investigating the feasibility of 7T body imaging have been developed and
demonstrated. Technology developments include a 300 MHz body coil, a
multi-channel surface coil, and a small, single channel surface coil.
Preliminary imaging results demonstrate whole body imaging at 7T with a
body coil, and with locally placed multi-channel transceiver coils and
B.sub.1 shimming. Models and measurements indicate that the conventional,
uniform, circularly polarized body coil may have limitations for
homogeneous excitation at 7T. Locally placed, multi-channel transceivers
may provide a solution to body coil shortcomings at 7T. Improvements in
both signal and homogeneity appear to be gained when using multi-channel
transceiver coils with B.sub.1 shimming for imaging local regions of
interest. Local, single channel surface coils may also be useful,
especially for superficial regions of interest. Cardiac and breast
imaging and spectroscopy appear to be early applications worth pursing at
7T. With the proper selection of coils and methods such as B.sub.1
shimming, body imaging in general may be feasible at 7T.

[0050]A new generation body coil platform could have a single RF body coil
form built to accommodate three functional configurations, such as, for
example, a single tuned, 32 element quadrature coil to be compatible with
CE's current 3T and 7T system products, a sixteen channel transmit coil
for B1 shimming, Parallel transmit (transmit SENSE) and other advanced
functions, and a sixteen channel transmit body coil together with a
sixteen element quadrature X nucleus coil such as 31P of great interest
in cardiac imaging applications. All three of these coil options would be
available in the same coil design and form factor, and could be pre-set
in the factory, or activated in the field. In some cases, this coil would
be combined with a gradient coil.

[0051]As used throughout this disclosure, the term quadrature excitation
is defined as circular polarization of coil's RF magnetic field. TEM is
defined as any electrical circuit capable of propagating a TEM wave, any
transmission line, such as, for example, striplines, microstrip, coax
lines, wave guides, cavities. Excitation is defined as transmit, drive,
or driven. Double tuned, dual tuned, multi-nuclear, and multiple tuned
describe a coil resonant or operational at more than one frequency.
Single tuned describes a coil is resonant or operational at a single
frequency. In a multi-channel coil, multiple coil elements are
independently capable of being driven and/or receiving. In a fixed mode
of operation, coil currents are not readily adjusted in coil after the
coil's configuration. Coil currents are adjustable in independent
elements of a multi-channel coil during the operation of the coil.
Coupling refers to mutual reactance or mutual inductance or mutual
capacitance between coil current elements. Lumped elements include
discrete capacitors and/or inductors. Conventional drive is driving
typically two or four elements (aka ports) of a "fixed" coil containing
more than the number of driven elements. A typical example would be a 16
element, quadrature birdcage or TEM coil driven at four symmetrically
spaced elements.

[0052]The disclosure should not be considered limited to the particular
examples described above, but rather should be understood to cover all
aspects of the invention as set out in the attached claims. Various
modifications, equivalent processes, as well as numerous structures to
which the invention can be applicable will be readily apparent to those
of skill in the art upon review of the instant specification.